Heat treating furnace



6, 1958 c. CONE ET AL HEAT TREATING FURNACE Filed April 6, 1955INVENTOR.

C. CO N E D. K. MARTIN ATTORNEY United States Patent C) burgh, Pa.,assignors to Surface Combustion Corpora= tion, Toledo, Ohio, acorporation of Ohio Application April 6, 1955, Serial No. 499,673

Claims. (Cl. 263-43) This invention pertains to the circulation of gasesin a heat treating furnace and more particularly to recirculation offlue products in a one-way fired soaking pit furnace.

Soaking pit furnaces are used to reheat partially chilled or cold steelingots to a uniform temperature for rolling. In operation, a number ofingots ordinarily are charged into the heating chamber and removedsingly for rolling after they have attained proper temperature.

The burner in a one-way fired pit-is generally located in the upperportion of an end wall and directs its flame toward the opposite end ofthe pit with its maximum heat concentration located near the oppositeend when the burner is firing at its full rate. The combustion gasesthen travel back through the lower portion of the pit and out throughexhaust ports located in the lower portion of i the end wall containingthe burner.

After placing the ingots in this heating chamber, or charging it, theburner is fired at its full rate until the desired maximum temperatureis approached. The firing rate is gradually decreased as the maximumtemperature is neared to avoid overshooting this temperature and to alsoenable more uniform heating to be attained by changing the area of heatconcentration as the burners firing rate decreases. When the desiredtemperature is reached, the burner will be shut off or adjusted to aminimum firing rate until the temperature controller again calls forfurther heating.

During the period in which the burner is old? or at minimum fire,combustion gases in the chamber become stagnant and the colder gasessettle toward the bottom of the chamber, thus establishing gaseouslayers of varying temperatures. These conditions tend to cause unevenheating of the ingots.

To overcome this problem, a novel means of recirculating gases when theheating burner is off or at its minimum firing rate is proposed. By suchmeans, gases will be circulated throughout the chamber to preventstagnation and maintain uniformity of pit temperatures.

We propose a method of heating a one-way fired soaking pit furnace byfiring a first burner until the soaking pit chamber reaches a controlpoint temperature. The firing rate of this burner will then besubstantially reduced and a second burner will be fired into anauxiliary combustion chamber. Flue gases will be emitted from a nozzlein this chamber through a duct and venturi tube to the soaking pitchamber, in a manner to induce recirculation of flue gases through theduct and soaking pit.

For further consideration of what we consider novel and our invention,refer to the accompanying drawings, description, and claims.

In the drawings:

Figure 1 represents a cross-section of a soaking pit 2,849,221 PatentedAug. 26, 1958 ICC furnace embodying the invention on line 1-1 of Fig ure2;

Figure '2 illustrates a cross-section of the soaking pit heating chamberon line 22 of Figure 1;

Figure 3 shows a cross section on line 3--3 of the apparatus of Figure 2showing a burner, recirculation apparatus, and mechanical control meanstherefor; and

Figure 4 represents a modification of Figure 3 showing electricalcontrol means.

In Figure 1 and Figure 2, heating chamber 11 comprises hearth 12, walls13, 14 and 15, and cover 16. Ingots 17 are placed in chamber 11 onhearth 12 to be heat treated. Supports 8 and 20 uphold the weight of thechamber 11 and ingots 17. Recess 21 accommodates a thermocouple orsimilar temperature responsive means.

Heating burner 22, represented by dotted lines in Figure 1, firesthrough burner port 23. Recirculating burnners 24 fire into combustionchambers 25. Combustion gases exit through nozzles 26, across ducts 27,and through venturi tubes 28. After circulating through chamber 11 in ahorse-shoe shaped path, indicated by arrows 39, these gases leavethrough exhaust ports 29. Part of these gases is then carried throughducts 27 and back through tubes 28 by an inspiration effect produced bythe high velocity combustion gases from chambers 25 passing throughtubes 28. The remaining gases travel through passage 30, tilerecuperator 31, metal recuperator 32, and out stack 33. High pressureair is blown by blower 34 through metal recuperator 32 and by-pass 35,if desired, duct 36, nozzle 37, and into venturi 38. Low pressure air,induced from the inspirating effect of jet pump 40, enters through tilerecuperator 31, passage 41, housing 42, and into venturi 38. The totalair then enters manifold 43 which may supply combustion air to a batteryof several pits. Duct 44 leads from this manifold to the heating burner22 on each pit. Air for the recirculating burners 24 is taken from thehigh pressure air in duct 36 and carried by pipes 45. Manifold 46supplies fuel to heating burner 22 and recirculating burners 24 by pipes47 and 48, respectively.

In Figure 3, a mechanical control means for controlling fuel or air tothe burners 22 and 24 is shown. Here valves 51 control the volume toburners 24 and valve 52 controls the volume to burner 22. These threevalves are operatively linked together by linkages 53 and 54. Anotherlinkage 55 connects one of the linkages with a power means such asservo-motor 56. This is regulated by a temperature control device 57responsive to a temperature responsive means such as a thermocouple (notshown) which may be placed in recess 21.

In operation the latter actuates servo-motor 56 which moves valves 51and 52 by means of linkages 53, 54,

and 55. When the soaking pit chamber temperature falls below thatrequired, instrument 57 actuates servomotor 56 which through theaforementioned linkages tends to open valve 52 and close valves 51.Likewise, when required temperature is again reached or exceeded, valves51 are caused to open and valve 52 to close. If the heating burner 22 isoperated in a graduated manner, as opposed to on-ofi', this controlsystem can function as a proportioning method.

An electrical control means for accomplishing the same results isillustrated in Figure 4. With this method, valve control motors 61 and62 actuate valves 63 and 64 through linkages 65 and 66. These motors 61and 62 are operated by relay 67 which is regulated by temperaturecontrol device 68 responsive to a temperature responsive means. Thiscontrol system operates on an on-ofl basis and does not function in aproportioning manner.

To those skilled in the art, other variations of this design will beapparent without changing the basic principles in our invention.

We claim:

l. The method of heating a soaking pit furnace which comprises: firing,a first burner, to,- produce flame in the.

heating chamber of said furnace until the temperature of said chamberrises to a. control point temperature; then substantially reducing thefiring rate; of said burner and firing a second burner into an auxiliarycombustion chamber and discharging therefrom a high velocity stream ofcombustion gas in inspirating relation to furnace gases venting from thefurnace; and directing the resulting admixture into said heating chamberto supply thereto a recirculating stream of heating gas while thefurnace is above the control point temperature.

2. In a soaking pit furnace, a. means for recirculating furnace gasescomprising: a tube opening; into the heating chamber in said furnace; aduct connecting the other end of said tube to another portion of thefurnace chamher; a combustion chamber located adjacent said tube andoutside said furnace chamber whose flue products emit through a noZZle,said duct, and said tube; a first burner adjacent said combustionchamber and capable of firing thereinto; a tile recuperator and metalrecuperator through which flue gases flow; means for creating a flow ofhigh pressure air through said metal recuperator; a duct for carryingsaid high pressure air to a jet pump after passing through said metalrecuperator, said jet pump inspirating low pressure air through saidtile recuperator; a second burner located adjacent said furnace chamberand capable of firing thereinto for heating said furnace chamber; a ductfor carrying the combined high pressure and low pressure air from saidjet pump to said second burner; a pipe connecting the high pressure airduct to said first burner; and a fuel supply for said first burner andsaid second burner.

3. In a soaking pit furnace, means for recirculating furnace gascomprising: a tube connecting a portion of a heating chamber in saidfurnace to a duct, said duct connecting said tube to another portion ofsaid heating chamber; a combustion chambe for directing products ofcombustion through said duct and said tube; a first burner for firinginto said combustion chamber; a high pressure air source; a jet pumpthrough which high pressure air flows, inspirating low pressure air froma low pressure air source; a second burner located adjacent said heatingchamber and capable of firing thereinto for heating said heatingchamber; a duct carrying the combined low and high pressure air mixtureto said second burner; a pipe carrying said high pressure air to saidfirst burner; 21 fuel supply source for supplying fuel to said firstburner and said second burner; and control means for alternating air andfuel flow to said first burner and to said second burner.

4. In a soaking pit furnace, means for recirculating furnace gascomprising: a tube connecting a portion of a heating chamber in saidfurnace to a duct, said duct connecting said tube to another portion ofsaid heating chamber; a combustion chamber for directing products ofcombustion through said duct and said tube; a first burner for firinginto said combustion chamber; a high pressure air source; a jet pumpthrough which high pressure air flows, inspirating low pressure air froma low pressure air source; a second burner located adjacent said heatingchamber and capable of firing thereinto for heating said heatingchamber; a duct carrying the combined low and high pressure air mixtureto said second burner; a pipe carrying said high pressure air to saidfirst burner; a fuel supply source for supplying fuel to said firstburner and said second burner; and control means for proportioning theflow of air and fuel to said first burner and said second burner todecrease the flow of said air and said fuel to one burner and toincrease the flow of said air and said fuel to the other burner.

5. The combination according to claim 3 wherein said control meanscomprises: means responsive to temperature in said heating chamber; atemperature control device responsive to said responsive means; andelectrically operated valves responsive to said control device 7 throughan electrical circuit for controlling flow of fuel to said burners.

6. The combination according to claim 4 wherein said control meanscomprises: means responsive to temperature in said heating chamber; atemperature control device responsive to said responsive means; a powermeans responsive to said control device; and a linked valve assemblyoperated by said power means for controlling flow of fuel to saidburners.

7. In a soaking pit furnace, apparatus for maintaining movement of thegases therein comprising: a tube connecting a portion of a heatingchamber in the furnace to a duct, said duct connecting said tube toanother portion of said heating chamber; a recirculating burner locatedoutside said chamber for directing a high velocity stream of gas throughsaid tube whereby gas in said duct is inspirated through said tube bysaid stream; a heating burner; a source of air; a source of combustiblegas; means responsive to the temperature in said chamber; a temperaturecontrol device responsive to said responsive means; and means responsiveto said device for directing gas and air to said heating burner when thetemperature of said chamber is below a predetermined point and to saidrecirculating burner when the temperature is above the predeterminedpoint.

8. In a soaking pit furnace, apparatus for maintaining movement ofthegases therein comprising: a tube connecting a portion of a heatingchamber in the furnace to a duct, said duct connecting said tube toanother portion of said heating chamber; a recirculating burner locatedoutside said chamber for directing a high velocity stream of gas throughsaid tube whereby gas in said duct is inspirated through said tube bysaid stream; a heating burner; a source of air; a source of combustiblegas; means responsive to the temperature in said chamber; a temperaturecontrol device responsive to said responsive means; and means responsiveto said device for proportioning air and gas to said recirculatingburner and said heating burner in a manner tending to direct a majorportion of the air and gas to said recirculating burner when thetemperature ofsaid chamber is above a predetermined point and to directa major portion of the air and gas to said heating burner when thetemperature of said chamber is below a predetermined point.

9. The method of heating a soaking pit furnace which comprises: firing afirst burner to produce fiame in the heating chamber of said furnaceuntil the temperature of said chamber rises to a control pointtemperature; then substantially reducing the firing rate of said burnerand firing a second burner into an auxiliary combustion chamber anddischarging therefrom a high velocity stream of combustion gas ininspirating relation to furnace gases venting from the furnace;directing the resulting admixture into said heating chamber to supplythereto a recirculating stream of heating gas; and controlling thefiring rate of said second burner to maintain the temperature of saidchamber substantially at control point temperature.

10. The method of heating a soaking pit furnace which comprises: firinga first burner to produce flame in the heating chamber of said furnaceuntil the temperature of said chamber rises to a control pointtemperature; then substantially reducing the firing rate of said burnerand firing a second burner into an auxiliary combustion chamber anddischarging therefrom a high velocity stream of combustion gas ininspirating relation to furnace gases venting from the furnace;directing the resulting admixture into said heating chamber to supplythereto a re- 2,329,211 Morton Sept. 14, 1943 circulating stream ofheating gas; and controlling the 2,414,888 Morton Jan. 28, 1947 firingrate of said second burner to fire alternately at a 2,504,320 GambleApr. 18, 1950 rate greater than the furnace holding rate and at a rate2,517,869 Grapp J Aug. 8, 1950 less than the furnace holding rate. 52,627,398 Hepburn Feb. 3, 1953 2,776,827 Graham Ian. 8, 1957 ReferencesCited in the file of 11118 patent 1 UNITED STATES PATENTS OTHERREFERENCES 1,729,763 De Florez Oct. 1, 1929 Industrial Furnaces (2ndEd.) by W. Trinks, John 2,085,811 Loftus July 6, 1937 10 Wiley and Sons,publisher, vol. 11 1942

